The present invention relates in general to motor vehicle headlamp systems, and, more specifically, to method and apparatus for aiming headlamps.
Motor vehicles use headlamps to illuminate the road. One or two pairs of headlamps are typically mounted at the left and right front sides of the vehicle. For example, a pair of low-beam headlamps and a pair of high-beam headlamps are used on some vehicles. Other vehicles may employ a single pair of headlamps that are electrically controlled to provide either low-beam or high-beam illumination.
Various regulations specify the light patterns that are to be produced by the headlamps. In particular, a beam cutoff (i.e., an upper border between illumination falling above and below a particular intensity) must be located at a certain height above the ground at a specified distance in front of the vehicle. In order to ensure compliance with regulations, headlamp mountings are made adjustable in order to aim the light beams as required. In general, a vehicle under test is put in a certain position relative to a test surface or measuring device, the headlamps are illuminated, and the resulting light pattern is analyzed. Based on the analysis, the headlamp mounting is adjusted either manually or automatically to reduce any error detected between the actual location of the beam and a desired beam location so that the desired cutoff is obtained. Headlamp aiming equipment (i.e., aimers) is available from many manufacturers which employ either projection analysis or direct measurement of the beam cutoff. Robotic mechanisms are also widely available for performing automatic adjustments.
It is well known that the actual intensity of light output from a headlamp is not perfectly constant. The intensity, and thus the precise beam pattern as detected by the aimer, varies in response to many different conditions that cannot be controlled or eliminated such as bulb-to-bulb differences, voltage fluctuations within the vehicle, engine on versus engine off voltages, obstructions in the light path, the presence of ambient lighting, variations in bulb mounting, and others. It is conventionally believed that the real-world aiming of the headlamp beam is relatively insensitive to these variations, and that the location of the horizontal cutoff would remain substantially constant. Nevertheless, headlamp aiming errors and inconsistencies have continued to be a common problem for vehicle manufacturers using the aimers that have been commercially available.